1. Field of the Invention
The present invention relates generally to tape cassettes and more particularly relates to a tape cassette having a light path for optically sensing the end of a magnetic tape.
2. Description of the Prior Art
A recording and/or reproducing apparatus, such as a videotape recorder or the like, is provided with a tape end sensing device having a light emitting element and a light receiving element for sensing the end of a magnetic tape. This type of recording and/or reproducing apparatus is constructed such that when a tape cassette is loaded into the apparatus, a lamp is inserted into the cassette housing. Light emitted from the lamp travels along a detection light path which intersects a predetermined tape path and passes through an opening formed in the side wall of the cassette housing to reach a photo cell provided as the light receiving element. When a transparent leader tape attached to the tape end crosses the detection light path, the light emitted from the lamp passes through the leader tape and is received by the light receiving element, thereby sensing the tape end. This can be used, for example, to stop a tape transport driving device.
Various types of tape cassettes are shown in the prior art for use with such a recording and/or reproducing apparatus. According to these proposals, a light-leading cover or tunnel piece is provided at the exit side of the lamp so that only light from the lamp which crosses the tape path is received by the light receiving element, and stray light other than that passing along the detection light path can be prevented from reaching the light receiving element.
For example, Japanese Utility Model Laid-Open Gazettes Nos. 62-51584 and 62-57983 and so on describe a first type of tape cassette, wherein the tunnel piece for introducing light from the lamp along the detection light path in the cassette housing is integrally formed with a lid lock member for a lid which opens and closes the tape mouth of the cassette housing, and a second type of tape cassette in which the tunnel piece is secured to the bottom portion of the cassette housing.
In the above-mentioned first type of tape cassette, the tunnel piece is formed as a protrusion only on the inner surface of the lid lock member. This allows an undesired external light which is incident on the detection light path to reach the light receiving element through a space between the bottom inside surface of the cassette housing and the inner surface of the lid lock member. This creates a substantial possibility that the tape end will be misdetected.
In the above-mentioned second type of tape cassette, in which the tunnel piece is secured to the bottom portion of the cassette housing, the outer end of the tunnel piece extends nearly to the side wall of the cassette housing, thereby preventing external light from being introduced into the detection light path. In this case, however, the assembly process for attaching the tunnel piece to the bottom portion of the cassette housing becomes cumbersome. In addition, a concave portion must be formed on the inside of the lid lock member in order to allow room for the tunnel piece. This has the disadvantage that the mechanical strength of the lid lock member will be decreased.